Powered pallet assemblies are used in industry for supporting and moving loads, workpieces or objects thereon. These devices are typically shaped as rectangular platforms which move either with their wheels running directly upon a floor surface or upon parallel tracks. Powered pallet assemblies are especially useful for material handling in industrial settings for transporting loads, particularly to and from various assembly work sites, production locations and warehouse sites. Powered pallet assemblies have on-board assemblies, as distinguished from non-powered pallets which must be pushed or pulled into position, and powered pallet assemblies may be either directly or remotely controlled.
A minimum amount of free floor space is typically available in production areas in factories and warehouses, and in other areas where powered pallet assemblies are commonly used. Consequently, powered pallet assemblies are commonly required to navigate through tight spaces and to make tight turns. The smaller the area of floor space in which these pallet assemblies are able to change their direction, the more efficient these assemblies become in their use of floor space. Consequently, a need exists for powered pallet assemblies, or motorized carriages, which are able to change their direction of movement in very tight spaces having minimal available floor space.
When making turns or changing directions, present powered pallet assemblies usually must be advanced forward somewhat when turning so as to enable steering along an arc. To increase the efficiency of the floor used by such powered pallet assemblies, this turning arc may be made tighter, but problems quickly develop when designing systems to enable a powered pallet assembly to turn through tighter and tighter arcs. What would instead be desired is a powered pallet assembly which is able to stop, make an abrupt change in its direction of motion, and then start moving in this new direction, all without having to steer or turn the pallet assembly through any arc.
To change directions, prior art powered pallet assemblies typically use their own internal steering systems, which change the direction in which the pallet assembly's wheels are facing, or they use trackways which the pallet assembly's wheels passively follow, thus avoiding the need for an active steering system. Both of these options suffer from their own particular disadvantages.
The design complexity and cost of a powered pallet assembly increase dramatically when an internal steering system is added to steer the wheels of the pallet as a way of changing the direction of motion. What is instead preferred is a pallet assembly which does not require a complex and expensive internal steering system with its accompanying internal guidance system. An inherent disadvantage of powered pallet systems which employs steerable pallets is that such systems typically employ a plurality of these expensive pallets. Thus, the overall system cost increases dramatically as the number of pallets in the system with steerable controls is increased.
Complex internal steering systems can be avoided through the use of guide-rails or trackways upon which the powered pallets travel. All that is required is some form of drive assembly to rotate the wheels of the pallet assembly, thus causing the pallet to move along the trackways. The pallet wheels passively follow the trackways which effectively steer the pallet assembly. Unfortunately, trackway-based pallet systems often suffer from the disadvantage of not being able to easily turn the pallet assembly in a very tight arc. In the system of U.S. Pat. No. 5,044,283, for example, cornering modules are provided to enable movement of motorized carriages through relatively tight curves. In other rail-based pallet systems, the corners simply are not very tight, and in still others, for example, the turntable type of system of U.S. Pat. No. 4,416,202, floor space is required to accommodate the structure necessary for rotation of the trackway.
Consequently, a type of compromise problem exists in choosing between and expensive pallet assemblies having internal steering systems, which will enable the pallet to change directions within a smaller area, and the less complex trackway-based pallet systems which are unable to change the direction of motion of the pallet assembly within a small area. What is desired, therefore, is a powered pallet assembly which is able to use the best features of both of these designs, in particular, the ability to change directions abruptly using only a minimum amount of floor space without requiring a complex internal steering or guidance system.
A further important limitation exists in many prior art pallet systems. Pallet assemblies which are able to make turns requiring only a minimum amount of floor space correspondingly turn the objects placed upon the pallets. This problem exists, for example, in the system of U.S. Pat. Nos. 5,044,283 and 4,416,202. Such changing of the workpiece or load orientation can cause problems in certain production operations since the turning of the objects supported by the pallet assembly during pallet turning may result in these objects being misoriented from one step in a production process to a subsequent step. Consequently, what is desired is the further advantage of a powered pallet assembly that is able to change its direction of motion without changing the orientation of the objects being transported.
U.S. Pat. Nos. 2,469,575, 3,094,941 and 3,356,039 disclose trackway mounted carriages or platforms which can abruptly change direction without changing the orientation of the load which they are carrying. In these systems, however, the load-supporting wheel assemblies are either very difficult to couple to an on-board motor for driving of the pallet through the support wheels, or the systems employ elaborate switch assemblies, or both. U.S. Pat. Nos. 989,759, 3,348,497 and 4,516,504 are examples of other switch assemblies employed in trackway-based transport systems.
A powered pallet assembly is needed, therefore, which is able to change its direction of movement in very tight spaces. Specifically, this new direction of motion should include angles of up to 90.degree. from the previous path of motion. The above should be done without having to steer the pallet assembly through any arc on the floor, and furthermore without the use of a complex internal steering apparatus, bulky turntables or complex switch assemblies. The pallet assembly further should be able to change its direction of motion without turning to face this new direction of motion, thus being able to move objects without rotating the orientation of the objects during changes of direction of the pallet assembly.
Still a further desirable feature of any powered pallet system is the ability to provide a system which will allow simultaneous operation of a large number of powered pallets. The pallets should be able to move around a trackway circuit and through various intersections in the circuit, with the movement of each of the pallets being individually controllable from a remote location, all while automatically preventing pallets from bumping into one another. Most preferably, such a system should not require complex communications apparatus on-board the pallets in order to be controlled by a central controller.